Conventionally, a lubrication structure is provided with first and second oil passage which are arranged to be overlapped with each other forming a double deck such that the first oil passage which guides the lubrication oil scooped up by the second pair of reduction gears into the catch tank is positioned lower than the position of the second oil passage which guides the lubrication oil scooped up by the first pair of reduction gears into the catch tank, due to the difference in scooping capacity of lubrication oil (capacity of scooping amount of oil) between the first and the second pairs of reduction gears, the second pair of reduction gears being inferior to the first pair of reduction gears. (See for example the Patent Document 1).